American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

Which of the following adjustments should NEVER be used to control brightness in a microscope?

1. The focus knob

2. Field diaphragm

3. Aperture diaphragm

4. Condenser position

The correct answer is: Aperture diaphragm

The aperture diaphragm is not the appropriate tool for controlling brightness in a microscope. Its main purpose is to regulate the amount of light that passes through the specimen by changing the diameter of the cone of light that hits the specimen. Adjusting the aperture diaphragm primarily affects contrast and resolution, rather than the overall brightness of the image. Using the aperture diaphragm to control brightness can lead to suboptimal imaging conditions, as it would not evenly distribute light across the field of view and could potentially degrade the quality of the image. Instead, the field diaphragm is specifically designed to limit the light entering the microscope, providing a method to adjust brightness effectively without compromising resolution or contrast. Meanwhile, adjusting the condenser position can help to enhance illumination and improve image clarity without altering the aperture dynamics. In summary, while brightness can be adjusted with other components such as the field diaphragm or the condenser, the aperture diaphragm is intended for light quality modification in relation to the sample being viewed and should not be used solely for brightness control.